Method and solution for treating metal surfaces



, Patented Apr. 1.0, 1934 UNITED s'rATes P TENT ()Fl-lCE N. J., assignors to Delaney Chemical Company, a corporation of Pennsylvania No Drawing. Application June 7, 1932,

. Serial no. 615,952

8 Claims. (o1; 14H) This invention is a method of so treating metals that thesurfaces thereof will be capable of taking a high polish.

One of the objects of the invention is to pro 'de 5 a method for treating metals, such as iron, steel,

zinc and alloys of zinc, chromium and aluminum, or either of them, so as to leave.a clean exposed area which will be capable of taking a high polish. A further object is to provide cleansed metal areas with surfaces which under the microscope. fail to showevidence of breaks or cracks, and having the'normal appearance of unpolished chromium, and which like chromium are capable of taking ahigh and durable polish. A further object is to provide a surface of the character mentioned which is free of oxides and other forms of corrosion, and which will provide a perfect bond for paint, enamel, lacquer, and metal plating. 'A further object is to so treat metal surfaces as to effectively degasify the metal in such manner that -more perfect electro-plating is possible than by the methods now in common use.- I

Theinvention will be hereinafter fully set forth and particularly pointed out in the claims.

In practice, the metal to be treated is dipped into or otherwise subjected to the action of a mixture containing copper salt, a nitrate and-an organic acid. Af-ter'said treatment the surfaces of the metal are washed in clear water, .or if desired it may be removed by any ordinarycleaning bath now in common use, after which it will beready for plating or buflingas the case may In practice, it is preferred to use a mixture of copper sulphate or chlorides or nitrates of copper, and nitrates such assodium nitrates and potassium nitrate. The organic acid preferred is oxalic vthe surface of the metal, the treated surface acid. The mixture is usually prepared in concentrated form designed to be diluted before be- 40 ing applied to the metal. In making the mixture weight:-

50% to 60% copper sulphate 30% to 35% sodium nitrate I 5% to 10% oxalic acid crystals.

of approximately the following proportions by The above mixture is'mixed with water in the approximate proportions by weight of 5% powder and 95% water. It has been found that the ingredients will dissolve quicker in warm water than in cold water, but where warm water is employed it is preferable'to use about one-half of the volume of water to dissolve the powderedmixture and then to add the balance of the water cold. The

' bath in its final form is used cold.

. .Just what'action takes place during the treat- '70 ment is not clearly understood, but the result is that the surfaces of the metal which have come intocontact with'the solution are cleansed of all surface corrosion and are left with non-corrosive clean surfaces which have somewhat the appearance of chromium before it is polished. Under the microscope the treated surface appears to exhibit to some extent, the nature of a continuous coating, but whether or not it is a coating has not yet been positivelydetermined, although under tests it maybe easily mistaken for chromium because of its similarity in appearance. It also possesses a definitev degasifying characteristic in connection with the electro-plating of metal in that it appears to completely dissipate the minute 5 gas deposits in the surface of the metal treated, so that-upon immersion into an electro-plating bath, the resistance to the adherence of the plate,

due to the presence. of gas pockets in the ordinary practice is completely avoided, and more uniform plating of the exposed surfaces is accomplished.

Upon removal of the chemical solution from presents a bright and clean appearance resemblingthat of chromium before polishing. Under the microscope it shows an apparently perfectly continuous coating-like surface extending over the entire treated area without any breaks, presenting a surface capable of withstanding bufiing polishing without breaking down. Its character is not easily determinable, and in fact is not sufiiciently distinguishable under chemical analysis and other tests to precisely determinewhether it is in the form of a coating, or is in fact a surface of the metal which has been treated. In any event, the exposed cleansed area should not be confused as a coating inthe sense of a painted or plated surface.

The treated surface as above stated has the an acid bath prior to electro-plating, oxides im-' mediately form on the surface, which prevent a perfect bond between the plate and the metal surface. A piece of metal treated by the process .hereinabove described is not open to any of these objections. This is because of the degasifying action and also because the original surface oxides and corrosions have been removed and the surface has been rendered chemically clean.'

Therefore, after said surface has been plated with other metals, thepeeling off of the plating as is a common experience under recognized plating processes does not occur, the bond between the coating and the treated surface becoming absolutely permanent. By reason of the production of the surface herein described, it is also possible to plate nickel and chromium directly on said surface without interposing an intermediate plating of copper as is now customary, so that a very considerable saving in time is accomplished in connection with electro-plating functions and a much more durable coating is obtained.

Having thus explained the nature of the invention and described an operative manner of constructing and using the same, although without attempting to set forth all ofthe forms in which it may be made, or all of the forms of its use, what is claimed is:-

1. .The method of treating metal surfaces comprising subjecting the surface to the action of a solution containing oxalic acid, a copper salt and an inorganic nitrate.

2. The method of treating metal surfaces 'com-' prising subjecting the surface to the action of a solution containing oxalic acid, a copper salt and an inorganic nitrate until a loose coating is formed thereon, and then removing said coating.

3. The method of treating metal surfaces comprising subjecting the surface to the action of a solution containing oxalic acid, a copper salt and an inorganic nitrate for a period of approximately two minutes, and then removing the coating produced by said mixture.

4. A solution for imparting'a polish-taking characteristic to metal surfaces comprising a mixture of oxalic acid, a copper salt and an inorganic nitrate.

5. A solution for imparting a polish-taking characteristic to metal surfaces comprising oxalic, acid, copper sulphate and an inorganic nitrate. v v

6. A solution for imparting a polish-taking characteristic to metal surfaces comprising oxalic acid, a copper salt and sodium nitrate.

'7. A solution for imparting a polish-taking characteristic to metal surfaces comprising .oxalic acid, copper sulphate and sodium nitrate.

8. In a material for treating metals so as to render them susceptible of taking a high polish comprising a water soluble mixture of not exceeding approximately 60% copper sulphate, not exceeding approximately 35% sodium nitrate and not exceeding 10% oxalic acid crystals.

OSCAR L. PETERSON. HARRY L; PETERSON. CLARENCE E. PETERSON. 

